1. Field of the Invention
This invention relates in general to magnetic recording and more particularly to apparatus/techniques for maximizing the storage capability of computer discs, especially floppy discs such as the now ubiquitous 51/4 inch floppy discs used in connection with the computer arts. By and large, state of the art floppy discs store about 0.5 megabytes of data.
2. Description Relative to the Prior Art
The packing density of data recorded on a magnetic medium is dependent to a large extent on the coercivity of the medium. Too low a coercivity allows demagnetization effects to alter closely packed recorded information, thereby rendering the information useless. For a medium of a certain coercivity, therefore, there is a minimum flux change length (fcl) that the medium will reliably support . . . which is to say that there is a maximum numer of data representative flux changes per inch (fci) that such a medium will permit.
In the interest of facilitating the teaching of the invention, a particular (representative) disc product, as well as the source of its otherwise attendant limited capacity, will now be discussed:
Given a 51/4 inch floppy disc, the information stored thereon being distributed among pie-shaped sectors (e.g. 78 in number), and the disc medium being coercivity-wise capable of supporting minimum bit lengths* of no less than, say, ##EQU1## an initial concern is: "What is the minimum disc radius R.sub.min that will be capable of recording bit lengths as little as 0.000046 inches?" FNT *"Bit length" as used herein is synonymous with flux change length", i.e. the maximum fci for the medium in question=21513. ##EQU2## Since the disc in question has an overall radius of 2.625", this leaves just one radial inch within which recording might be made.
Assuming that a peripheral band about four tenths of a radial inch is needed to effect good head-to-media interface at the outer regions of the disc, recording is limited to a region of only 0.6 radial inches. With the medium capable of recording, say, 333 tracks per inch, the disc, structured as described above, is thus limited to 200 effective recording tracks, i.e. EQU 333.times.0.6=200
The per-side data storage capacity C.sub.s of the disc so described is therefore: ##EQU3##
By recording on both disc sides, the total capacity C.sub.2s increases to 8 megabytes.